An FFV (Flexible Fuel Vehicle) using a fuel made of a blend of gasoline and alcohol (ethanol) or a fuel made of alcohol only (these fuels are hereinafter also referred to as alcohol fuel) has been known. The alcohol fuel is different in characteristics from gasoline. For example, the alcohol fuel has a higher octane number than gasoline, and is therefore less likely to cause knocking. Accordingly, in the case where the alcohol fuel is used, it is preferable to control the ignition timing of the internal combustion engine in a manner different from the case where only the gasoline is used as fuel. For example, in order to improve the output of the internal combustion engine, the ignition timing may be advanced for a higher alcohol concentration relative to the ignition timing for a lower alcohol concentration.
Japanese Patent Laying-Open No. 5-33748 discloses an engine ignition timing control apparatus for an engine using an alcohol fuel, with which the output and fuel economy can be improved without causing knocking. The ignition timing control apparatus disclosed in Japanese Patent Laying-Open No. 5-33748 includes an engine speed detection unit for detecting the engine speed, an ignition timing control unit for controlling the ignition timing of the engine based on an output of the engine speed detection unit, an alcohol concentration detection unit for detecting the alcohol concentration of a fuel in use, and an ignition timing correction unit for correcting, based on respective outputs of the engine speed detection unit and the alcohol concentration detection unit, the ignition timing set by the ignition timing control unit by advancing the set ignition timing when the engine speed is low and the alcohol concentration is high.
The ignition timing control apparatus disclosed in the above-referenced publication corrects the ignition timing by advancing the ignition timing when the engine speed is low and the alcohol concentration in the fuel in use is high, relative to the ignition timing when the alcohol concentration is low. The ignition timing is thus appropriately controlled when the engine speed is low. The output and fuel economy can accordingly be improved without causing knocking.
As for refueling, the fuel supplied for refueling does not always have the same alcohol concentration. For example, an alcohol fuel of a lower alcohol concentration than that of the alcohol fuel remaining in the fuel tank could be supplied for refueling. In such a case, the octane number suddenly decreases. While Japanese Patent Laying-Open No. 5-33748 discloses that the ignition timing is set according to the detected alcohol concentration, it takes some time to detect the alcohol concentration. Therefore, if an alcohol fuel of a lower alcohol concentration is supplied for refueling, the ignition timing could be advanced until the detection of the alcohol concentration is completed and until knocking occurs.